Method of making paper

ABSTRACT

A method of making paper includes adding to an aqueous slurry containing pulp fibers a polymer latex binder that has a copolymer obtained by polymerizing one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to 35. In some implementations, the carbohydrate derived compound can include dextrins, maltodextrins, or mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/345,343, filed on May 17, 2010, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure relates to papermaking and more particularly to a method of making paper that includes adding a polymer latex binder derived from a carbohydrate derived compound to an aqueous slurry to form paper.

BACKGROUND

Papermaking is a process of introducing an aqueous slurry of pulp or wood cellulosic fibers onto a screen or similar device so that the water can be removed, thereby forming a sheet of consolidated fibers, which upon pressing and drying can be processed into dry roll or sheet form. Typically, in papermaking, the feed or inlet to the paper machine is an aqueous slurry or water suspension of pulp fibers, which can be provided from a wet end system. In the wet end, the pulp along with other additives can be mixed in an aqueous slurry and subjected to mechanical and other operations such as beating and refining to improve interfiber bonding and other physical properties of the finished sheet. Additives commonly introduced along with the pulp fibers may include pigments such as titanium dioxide, mineral fillers such as clay and calcium carbonate, and other materials introduced into paper to achieve properties such as improved brightness, opacity, smoothness, ink receptivity, fire retardancy, water resistance, and increased bulk.

SUMMARY

A polymer latex binder is described that has a copolymer of one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to 35 such as a dextrin or maltodextrin. The polymer latex binder can be used in a wet end application of a papermaking process. Paper sheets made with the polymer latex binder can have enhanced dry paper strength, even in the presence of relatively high filler contents.

In one aspect, a method of making paper can include mixing a polymer latex binder with an aqueous suspension that has pulp fibers. The polymer latex binder can include a copolymer that is obtained by polymerizing one or more unsaturated monomers and a carbohydrate derived compound that has a dextrose equivalent (DE) of 10 to 35. The method can also include removing water from the mixture of the aqueous suspension and the polymer latex binder and forming the paper.

In various implementations, the mixture of the aqueous suspension and the polymer latex binder can be dried to form paper. The polymer latex binder can be prepared by copolymerizing in an aqueous medium a mixture of the one or more unsaturated monomers and the carbohydrate derived compound. The one or more unsaturated monomers can be present in an amount of greater than 60 wt % based on total monomer weight. The carbohydrate derived compound can be present in an amount of less than 50 wt % based on total monomer weight (e.g. 5 to 45 wt %). The copolymer can be present in an amount of 2 to 12 wt % of the solids content based on the total solids content of the mixture of the aqueous slurry and the polymer latex binder. The copolymer can include a pure acrylic copolymer, a styrene acrylic copolymer, a styrene butadiene copolymer, or a vinyl acrylic copolymer. The one or more unsaturated monomers can include an ethylenically unsaturated monomer. The carbohydrate derived compound can be selected from the group consisting of dextrins, maltodextrins, and mixtures thereof. The carbohydrate derived compound can have a weight average molecular weight of 3000 to 20,000. The carbohydrate derived compound can be soluble in water at room temperature in an amount of greater than 40% by weight. A solution of the carbohydrate derived compound in an amount of 50% by weight in water at room temperature can have a viscosity of 100 to 1000 cps. The carbohydrate derived compound can have a non-uniformity of 6 to 12. The carbohydrate derived compound can be chemically modified by etherification or esterification. One or more additional binders can be added to the mixture of the aqueous suspension and the polymer latex binder. One or more cationic retention aids can also be added to the mixture. The aqueous suspension can have less than 2 wt % solids when the polymer latex binder is added. The polymer latex binder can be added at a temperature of 40° C. to 80° C.

In another aspect, a paper sheet can include a matrix of pulp fibers that has a copolymer uniformly dispersed throughout. The copolymer can be derived from one or more unsaturated monomers and a carbohydrate derived compound that has a dextrose equivalent (DE) of 10 to 35.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1-5 show tensile strength for various papers prepared according to working and comparative examples.

DETAILED DESCRIPTION

The term “comprising” and variations thereof as used herein are used synonymously with the term “including” and variations thereof and are open, non-limiting terms. The term “paper” as used herein describes cellulosic materials such as newsprint, SC paper (super-calendered paper), wood-free or wood-containing writing and printing paper, paperboard, cardboard, linerboard, corrugating medium, tissue, toweling, and the like.

A method of making paper is described that includes adding to an aqueous suspension containing pulp fibers a polymer latex binder comprising a copolymer obtained by polymerization of one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to 35 to form a mixture thereof. The method also includes removing water from the mixture of the aqueous suspension and the polymer latex binder and forming paper. For example, the paper can be formed (e.g. into a sheet) and the aqueous pulp suspension can be dried. The resultant paper can have increased paper properties such as enhanced dry paper strength.

The copolymer can be a pure acrylic copolymer, a styrene acrylic copolymer, a styrene butadiene copolymer, or a vinyl acrylic copolymer. Suitable unsaturated monomers for use in forming the copolymer are generally ethylenically unsaturated monomers and include vinylaromatic compounds (e.g. styrene, α-methylstyrene, o-chlorostyrene, and vinyltoluenes); 1,2-butadiene (i.e. butadiene); conjugated dienes (e.g. 1,3-butadiene and isoprene); α,β-monoethylenically unsaturated mono and dicarboxylic acids or anhydrides thereof (e.g. acrylic acid, methacrylic acid, crotonic acid, dimethacrylic acid, ethylacrylic acid, allylacetic acid, vinylacetic acid maleic acid, fumaric acid, itaconic acid, mesaconic acid, methylmalonic acid, citraconic acid, maleic anhydride, itaconic anhydride, and methylmalonic anhydride); esters of α,β-monoethylenically unsaturated mono and dicarboxylic acids having 3 to 6 carbon atoms with alkanols having 1 to 12 carbon atoms (e.g. esters of acrylic acid, methacrylic acid, maleic acid, fumaric acid, or itaconic acid, with C1-C12, C1-C8, or C1-C4 alkanols such as ethyl, n-butyl, isobutyl and 2-ethylhexyl acrylates and methacrylates, dimethyl maleate and n-butyl maleate); acrylamides and alkyl-substituted acrylamides (e.g. (meth)acrylamide, N-tert-butylacrylamide, and N-methyl(meth)acrylamide); (meth)acrylonitrile; vinyl and vinylidene halides (e.g. vinyl chloride and vinylidene chloride); vinyl esters of C1-C18 mono or dicarboxylic acids (e.g. vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl laurate and vinyl stearate); C1-C4 hydroxyalkyl esters of C3-C6 mono or dicarboxylic acids, especially of acrylic acid, methacrylic acid or maleic acid, or their derivatives alkoxylated with from 2 to 50 moles of ethylene oxide, propylene oxide, butylene oxide or mixtures thereof, or esters of these acids with C1-C18 alcohols alkoxylated with from 2 to 50 moles of ethylene oxide, propylene oxide, butylene oxide or mixtures thereof (e.g. hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and methylpolyglycol acrylate); and monomers containing glycidyl groups (e.g. glycidyl methacrylate).

Additional monomers that can be used include linear 1-olefins, branched-chain 1-olefins or cyclic olefins (e.g., ethene, propene, butene, isobutene, pentene, cyclopentene, hexene, and cyclohexene); vinyl and allyl alkyl ethers having 1 to 40 carbon atoms in the alkyl radical, wherein the alkyl radical can possibly carry further substituents such as a hydroxyl group, an amino or dialkylamino group, or one or more alkoxylated groups (e.g. methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, isobutyl vinyl ether, 2-ethylhexyl vinyl ether, vinyl cyclohexyl ether, vinyl 4-hydroxybutyl ether, decyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2-(diethylamino)ethyl vinyl ether, 2-(di-n-butylamino)ethyl vinyl ether, methyldiglycol vinyl ether, and the corresponding allyl ethers); sulfo-functional monomers (e.g. allylsulfonic acid, methallylsulfonic acid, styrenesulfonate, vinylsulfonic acid, allyloxybenzenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and their corresponding alkali metal or ammonium salts, sulfopropyl acrylate and sulfopropyl methacrylate); vinylphosphonic acid, dimethyl vinylphosphonate, and other phosphorus monomers; alkylaminoalkyl (meth)acrylates or alkylaminoalkyl(meth)acrylamides or quaternization products thereof (e.g. 2-(N,N-dimethylamino)ethyl (meth)acrylate, 3-(N,N-dimethylamino)propyl (meth)acrylate, 2-(N,N,N-trimethylammonium)ethyl (meth)acrylate chloride, 2-dimethylaminoethyl(meth)acrylamide, 3-dimethylaminopropyl(meth)acrylamide, and 3-trimethylammoniumpropyl(meth)acrylamide chloride); allyl esters of C1-C30 monocarboxylic acids; N-Vinyl compounds (e.g. N-vinylformamide, N-vinyl-N-methylformamide, N-vinylpyrrolidone, N-vinylimidazole, 1-vinyl-2-methylimidazole, 1-vinyl-2-methylimidazoline, N-vinylcaprolactam, vinylcarbazole, 2-vinylpyridine, and 4-vinylpyridine); monomers containing 1,3-diketo groups (e.g. acetoacetoxyethyl(meth)acrylate or diacetonacrylamide; monomers containing urea groups (e.g. ureidoethyl (meth)acrylate, acrylamidoglycolic acid, and methacrylamidoglycolate methyl ether); and monomers containing silyl groups (e.g. trimethoxysilylpropyl methacrylate).

The monomers can also include one or more crosslinkers such as N-alkylolamides of α,β-monoethylenically unsaturated carboxylic acids having 3 to 10 carbon atoms and esters thereof with alcohols having 1 to 4 carbon atoms (e.g. N-methylolacrylamide and N-methylolmethacrylamide); glyoxal based crosslinkers; monomers containing two vinyl groups; monomers containing two vinylidene groups; and monomers containing two alkenyl groups. Exemplary crosslinking monomers include diesters of dihydric alcohols with α,β-monoethylenically unsaturated monocarboxylic acids, of which in turn acrylic acid and methacrylic acid can be employed. Examples of such monomers containing two non-conjugated ethylenically unsaturated double bonds are alkylene glycol diacrylates and dimethacrylates, such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate and propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallyl fumarate and methylenebisacrylamide. In some embodiments, the crosslinking monomers include alkylene glycol diacrylates and dimethacrylates, and/or divinylbenzene. The crosslinking monomers when used in the copolymer can be present in an amount of from 0.2% to 5% by weight based on the weight of the total monomer and are considered part of the total amount of monomers used in the copolymer.

In addition to the crosslinking monomers, small amounts (e.g. from 0.01 to 4% by weight based on the total monomer weight) of molecular weight regulators, such as tert-dodecyl mercaptan, can be used. Such substances are preferably added to the polymerization zone in a mixture with the monomers to be polymerized and are considered part of the total amount of unsaturated monomers used in the copolymer.

In some embodiments, the unsaturated monomers can include styrene, α-methylstyrene, (meth)acrylic acid (i.e., acrylic acid and/or methacrylic acid), itaconic acid, maleic acid, fumaric acid, crotonic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, vinyl acetate, butadiene, (meth)acrylamide, (meth)acrylonitrile, hydroxyethyl (meth)acrylate and glycidyl (meth)acrylate.

In some embodiments, the copolymer can be a styrene acrylic copolymer derived from unsaturated monomers including styrene, (meth)acrylic acid, (meth)acrylic acid esters, (meth)acrylamide, (meth)acrylonitrile, and mixtures thereof. For example, the styrene acrylic copolymer can include styrene and at least one of (meth)acrylic acid, itaconic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate. The unsaturated monomers of the styrene acrylic copolymer can include from 39 to 69% by weight of (meth)acrylates, from 30 to 60% by weight of styrene, 0 to 3% by weight of (meth)acrylamide, and 0 to 10% by weight of (meth)acrylonitrile. The unsaturated monomers of the styrene acrylic copolymer can also include from 0 to 5% by weight of one or more crosslinking monomers as described above such as alkylene glycol diacrylates and dimethacrylates.

In some embodiments, the copolymer can be pure acrylic copolymer derived from one or more unsaturated monomers including (meth)acrylic acid, (meth)acrylic acid esters, (meth)acrylamide, (meth)acrylonitrile, and mixtures thereof. For example, the pure acrylic copolymer can include at least one of (meth)acrylic acid, itaconic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate. In some embodiments, the unsaturated monomers of the pure acrylic copolymer can include from 76 to 100% of at least one (meth)acrylic acid ester (e.g. 90 to 99%); 0 to 6% of itaconic acid and/or meth(acrylic) acid; 0 to 3% of at least one (meth)acrylamide, and 0 to 10% of at least one (meth)acrylonitrile. The styrene acrylic copolymer can also include from 0 to 5% by weight of one or more crosslinking monomers as described above such as alkylene glycol diacrylates and dimethacrylates.

In some embodiments, the copolymer can be a styrene butadiene copolymer derived from unsaturated monomers including styrene, butadiene, (meth)acrylamide, (meth)acrylonitrile, itaconic acid and (meth)acrylic acid. The unsaturated monomers of the styrene butadiene copolymer can include from 40 to 75% by weight of styrene, from 25 to 60% by weight of butadiene, 1 to 10% of itaconic and/or (meth)acrylic acid, 0 to 3% by weight of (meth)acrylamide, and 0 to 20% by weight (meth)acrylonitrile. The styrene butadiene copolymer can also include from 0 to 5% by weight of one or more crosslinking monomers as described above such as divinylbenzene.

In some embodiments, the copolymer is derived from the unsaturated monomers in an amount of from greater than 50 to less than 100 wt %, 55 to 95 wt %, 60 to 92 wt %, or 65 to 85 wt %, based on the total monomer weight (or dry polymer weight in the paper).

In addition to the unsaturated monomers, the copolymer is formed from a carbohydrate derived compound. The carbohydrate derived compound can have a dextrose equivalent (DE) of 10 to 35, 12.5 to 25, or 15 to 20. The DE value can be determined in accordance with the Lane and Eynon test method (International Standard ISO 5377:1981). The weight average molecular weight (M_(w)) of the carbohydrate derived compound can be 3000 to 20,000, 5000 to 17,000, or 8000 to 14,000. The weight average molecular weight data can be determined using gel permeation chromatography (GPC). The carbohydrate derived compound can be soluble in water at room temperature (e.g., 25 degree C.) in an amount of greater than 40%, greater than 50%, or greater than 60% by weight, or can even be completely soluble in water at room temperature. Solutions of the carbohydrate derived compound in an amount of 50% by weight in water at room temperature can have a viscosity of 100 to 1000 cps, or 200 to 500 cps.

In some embodiments, the carbohydrate derived compound can include dextrins, maltodextrins, or mixtures thereof. The dextrins, maltodextrins, or mixtures thereof can have the DE's, molecular weights, water solubilities, and viscosities described above. The dextrins and maltodextrins are generally degraded starches whose degradation is effected by heating with or without addition of chemicals, it being possible to recombine degradation fragments under the degradation conditions to form new bonds which were not present in this form in the original starch. Roast dextrins such as white and yellow dextrins that are prepared by heating moist-dry starch, usually in the presence of small amounts of acid, are less preferred. The carbohydrate derived compound can be prepared as described in Guinther Tegge, Starke and Starkederivate, Behr's Verlag, Hamburg 1984, p. 173 and p. 220 ff and in EP 441 197.

The carbohydrate derived compound can be prepared from any native starches, such as cereal starches (e.g. corn, wheat, rice or barley), tuber and root starches (e.g. potatoes, tapioca roots or arrowroot) or sago starches. The carbohydrate derived compound can also have a bimodal molecular weight distribution and can have a weight average molecular weight as described above. The carbohydrate derived compound can have a nonuniformity U (defined as the ratio between the weight average weight M_(w) and the number average molecular weight M_(n)) that characterizes the molecular weight distribution in the range from 6 to 12, from 7 to 11 or from 8 to 10. The proportion by weight of carbohydrate derived compound having a molecular weight of below 1000 can be from 10% to 70% by weight, or 20 to 40% by weight. In some embodiments, the carbohydrate derived compound in a 40% strength by weight aqueous solution can have a dynamic viscosity η⁴⁰ [Pa·s], determined in accordance with DIN 53 019 at 25° C. and a shear gradient of 75 s⁻¹, of from 0.01 to 0.06, 0.015 to 0.04, or 0.02 to 0.035.

In some embodiments, the carbohydrate derived compound can be chemically modified such as by etherification or esterification. The chemical modification can be carried out in advance on a starting starch before its degradation. Esterification is possible using both inorganic and organic acids, or anhydrides or chlorides thereof. Phosphated and acetylated degraded starches can also be used. The most common method of etherification is treatment with organohalogen compounds, epoxides or sulfates in aqueous alkaline solution. The ethers can be alkyl ethers, hydroxyalkyl ethers, carboxyalkyl ethers and allylethers.

The copolymer can be derived from greater than 0 to less than 50 wt %, 5 to 45 wt %, 8 to 40 wt %, or 15 to 35 wt %, of the carbohydrate derived compound based on the total monomer weight (or dry polymer weight in the paper).

In some implementations, the papermaking method described herein can include providing the polymer latex binder by polymerizing in an aqueous medium a mixture of the unsaturated monomer(s) and the carbohydrate derived compound to produce the copolymer.

The polymer latex binder can be prepared by polymerizing the unsaturated monomers using free-radical aqueous emulsion polymerization in the presence of the carbohydrate derived compound. Suitable methods are described in U.S. Pat. No. 6,080,813, which is hereby incorporated by reference in its entirety. The emulsion polymerization temperature is generally from 30 to 95° C. or from 75 to 90° C. The polymerization medium can include water alone or a mixture of water and water-miscible liquids, such as methanol. In some embodiments, water is used alone. The emulsion polymerization can be carried out either as a batch process or in the form of a feed process, including a step or gradient procedure. In some embodiments, a feed process is used in which part of the polymerization batch is heated to the polymerization temperature and partially polymerized, and the remainder of the polymerization batch is subsequently fed to the polymerization zone continuously, in steps or with superposition of a concentration gradient, usually via a plurality of spatially separate feed streams, of which one or more contain the monomers in pure or emulsified form, while maintaining the polymerization. The initially introduced mixture and/or the monomer feed stream can contain small amounts of emulsifiers, generally less than 0.5% by weight, based on the total amount of monomers to be polymerized. The monomers can be frequently fed to the polymerization zone after pre-emulsification with these assistant emulsifiers. The feed process can be designed by initially introducing the entire carbohydrate derived compound to be used in dissolved form in an aqueous mixture. This means that the aqueous solution produced on partial hydrolysis of the starting starch can, after the hydrolysis has been terminated to form the carbohydrate derived compound, for example by neutralization of the catalytic acid and cooling, be further used directly for the aqueous emulsion polymerization. Prior isolation of the carbohydrate derived compound, for example by spray drying, is unnecessary but can also be used.

The free-radical emulsion polymerization can be carried out in the presence of a free-radical polymerization initiator. The free-radical polymerization initiators that can be used in the process are all those which are capable of initiating a free-radical aqueous emulsion polymerization including alkali metal peroxydisulfates and H₂O₂, or azo compounds. Combined systems can also be used comprising at least one organic reducing agent and at least one peroxide and/or hydroperoxide, e.g., tert-butyl hydroperoxide and the sodium metal salt of hydroxymethanesulfinic acid or hydrogen peroxide and ascorbic acid. Combined systems can also be used additionally containing a small amount of a metal compound which is soluble in the polymerization medium and whose metallic component can exist in more than one oxidation state, e.g., ascorbic acid/iron(II) sulfate/hydrogen peroxide, where ascorbic acid can be replaced by the sodium metal salt of hydroxymethanesulfinic acid, sodium sulfite, sodium hydrogen sulfite or sodium metal bisulfite and hydrogen peroxide can be replaced by tert-butyl hydroperoxide or alkali metal peroxydisulfates and/or ammonium peroxydisulfates. In the combined systems, the carbohydrate derived compound can also be used as the reducing component. In general, the amount of free-radical initiator systems employed is from 0.1 to 2% by weight, based on the total amount of the monomers to be polymerized. In some embodiments, the initiators are ammonium and/or alkali metal peroxydisulfates (e.g. sodium peroxydisulfates), alone or as a constituent of combined systems.

The manner in which the free-radical initiator system is added to the polymerization reactor during the free-radical aqueous emulsion polymerization is not critical. It can either all be introduced into the polymerization reactor at the beginning, or added continuously or stepwise as it is consumed during the free-radical aqueous emulsion polymerization. In detail, this depends in a manner known to an average person skilled in the art both from the chemical nature of the initiator system and on the polymerization temperature. In some embodiments, some is introduced at the beginning and the remainder is added to the polymerization zone as it is consumed. It is also possible to carry out the free-radical aqueous emulsion polymerization under superatmospheric or reduced pressure.

The polymer latex binder can be prepared with a solid content of from 10 to 75% by weight, 15 to 65% by weight, or 20 to 60% by weight. The copolymer can be present in an amount of 2 to 12 wt %, 4 to 10 wt %, or 6 to 9 wt % of the solid content of the solids content of the mixture of the aqueous suspension and the polymer latex binder. The polymer latex binder can then be concentrated if desired to provide a total solid content of 40-75% by weight. The polymer latex binder can be converted, in a manner known per se, to redispersible polymer powders (e.g., spray drying, roll drying or suction-filter drying). If the polymer latex binder is to be dried, drying aids can be used. The copolymers have a long shelf life and can be redispersed in water for use in the paper coating or binding formulation.

In some embodiments, the polymer latex binder contains no or substantially no polyvinyl alcohol, carboxylmethylcellulose, polyvinylpyrrolidone and water-insoluble starches.

In some implementations, the method can include the addition of one or more polymer binders that have not been derived from the carbohydrate derived compound. The polymer binder can be a pure acrylic copolymer, styrene acrylic copolymer, styrene butadiene copolymer, vinyl acrylic copolymer, or a mixture thereof. For example, a styrene acrylic copolymer or a styrene butadiene copolymer could be included.

In some implementations, the method can include the addition of fillers. Fillers can be added to impart certain properties to the paper such as smoothness, whiteness, increased density or weight, decreased porosity, increased opacity, flatness, glossiness, and the like. Suitable fillers include calcium carbonate (precipitated or ground), kaolin, bentonite, or other clays; talc; diatomaceous earth; mica; barium sulfate; magnesium carbonate; vermiculite; graphite; carbon black; alumina; silicas (fumed or precipitated in powders or dispersions); colloidal silica; silica gel; titanium oxide; aluminum hydroxide; aluminum trihydrate; satine white; magnesium oxide; plastic pigments; white urea resin pigments; and rubber powder. In some embodiments, the paper can have a filler content of 4 to 60% by weight based on dried paper stock. In some embodiments, the paper can have a filler content of 5 to 40 wt %.

In some implementations, the method can include the addition of one or more cationic retention aids to increase the retention of fillers in paper. Suitable cationic retention aids include polyethylene amides or modified polyamides, poly-diallyl-dimethyl ammonium chloride (poly-DADMAC), dimethylamine/epichlorohydrin resins, epichlorohydrin/polyamidoamine resins, polyethyleneimines, aluminum sulphonate (Alum) or poly-aluminum chloride. For example, a polyethyleneimine commercially available under the POLYMIN trademark from BASF Corporation can be used as a cationic retention aid. The retention aids can be added to the paper stock in the aqueous slurry along with the polymer latex binder and any other wet end additives. The cationic retention aid can be added in an amount of from 0.01% to 2%, from 0.05 to 1%, or from 0.1 to 0.5% (e.g. 0.3%), based on the total pulp content present in the aqueous suspension.

In some implementations, the method can include the addition of dyes and/or pigments to produce colored or patterned paper. Exemplary dyes include basic dyes, acid dyes, anionic direct dyes, cationic direct dyes, anionic pigment dispersions, and cationic pigment dispersions. Various organic pigments and inorganic pigments can be used as coloring agents including non-toxic anticorrosive pigments. Examples of such pigments include phosphate-type anticorrosive pigments such as zinc phosphate, calcium phosphate, aluminum phosphate, titanium phosphate, silicon phosphate, and ortho and fused phosphates of these; molybdate-type anticorrosive pigments such as zinc molybdate, calcium molybdate, calcium zinc molybdate, potassium zinc molybdate, potassium zinc phosphomolybdate and potassium calcium phosphomolybdate; and borate-type anticorrosive pigments such as calcium borate, zinc borate, barium borate, barium meta-borate and calcium meta-borate.

In some implementations, the method can include the addition of a thickener. Suitable thickeners include (meth)acrylic acid/alkyl (meth)acrylate copolymers (e.g. Sterocoll® FD thickener and Sterocoll® FS thickener, both of which are commercially available from BASF Corporation), hydroxyethyl cellulose, guar gum, jaguar, carrageenan, xanthan, acetan, konjac mannan, xyloglucan, urethanes and mixtures thereof. The thickener can be added to the formulation as an aqueous dispersion or emulsion, or as a solid powder.

In some implementations, the method can include the addition of other additives. The additives can be any additives that can be generally included in a papermaking process. Further additives include surfactants, wetting agents, protective colloids, biocides, dispersing agents, thixotropic agents, freeze store stability additives, pH adjusting agents, corrosion inhibitors, ultraviolet light stabilizers, crosslinkers, crosslinking promoters, and lubricants.

In some embodiments, the polymer latex binder is added in a wet end application where in the aqueous suspension include less than 2 wt % solids (i.e., pulp fibers and optionally fillers and other additives) and greater than 98 wt % water (e.g. 1 wt % solids and 99% water). Suitable pulp fibers can include bleached and unbleached Kraft pulps, bleached and unbleached sulfite and sulfate pulps, thermomechanical, chemithermomechanical and mechanical pulps, groundwood pulps, and recycled pulps. The polymer latex binder can be added in an amount of from 0.1% to 10%, from 0.5 to 7.5%, from 1 to 6%, or from 3 to 5%, based on the total pulp content present in the aqueous suspension.

The polymer latex binder can be added to the aqueous suspension at any suitable temperatures. For example, the polymer latex binder can be added at a temperature of from room temperature to less than 100° C., from 40° C. to 80° C., or from 45° C. to 70° C.

In some embodiments, it may be desirable to increase the filler content of the paper. However, increased filler content may result in a decrease in the dry strength of paper. The papermaking method described herein can advantageously use relatively high filler contents without substantially impairing the dry strength of the resulting paper. Alternately, the papermaking method described herein can include typical filler contents and can be used to increase the dry strength of the paper.

When papers produced using the method described herein are used in printing or copying process, reduced dust formation and a lower level of deposition on the rollers can be observed. Due to their relatively high strength, papers produced using the method described herein can be produced without further surface finishing being carried out in the size press.

The paper sheet can include a matrix of pulp fibers having a copolymer uniformly dispersed throughout. The copolymer is derived from one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to 35. Suitable unsaturated monomers and carbohydrate derived compounds are discussed herein. In some embodiments, the dry strength of the paper sheet can be increased by 5-300% or more over compositions that do not include the polymer latex binder described herein.

EXAMPLES

The following examples are provided to more fully illustrate some of the embodiments of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. Parts and percentages are provided on a per weight basis except as otherwise indicated.

Working Examples 1-3 & Comparative Examples 1-5

An aqueous suspension having 50 parts of Kraft pulp and 50 parts of groundwood pulp was prepared at 1% solids. 16 parts of precipitated calcium carbonate (PCC) were added to the aqueous suspension for paper glossiness. 3 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 (a styrene/butyl acrylate copolymer dispersion that is derived from 23% maltodextrin and commercially available from BASF Corporation) were added to the aqueous suspension as a polymer latex binder in Working Examples 1-3. 3 parts dry polymer based on the amount of dry cellulosic material of Acronal® 5728 NA (a styrene/butyl acrylate copolymer dispersion commercially available from BASF Corporation) were added to the aqueous suspension as a polymer latex binder in Comparative Examples 1-2. 3 parts dry polymer based on the amount of dry cellulosic material of Acronal® 5504 NA (a styrene/butyl acrylate/acrylonitrile copolymer dispersion commercially available from BASF Corporation) were added to the aqueous suspension as a polymer latex binder in Comparative Examples 3-4. No polymer latex binder was used in Comparative Example 5. For Working Examples 2-3 and Comparative Examples 2 and 4, the polymer latex binders were added at 50° C. For the other examples, the polymer latex binders were added at room temperature. 0.3 parts based on the amount of copolymer dispersion added of Polymin® SNA (a polyethyleneimine cationic retention aid commercially available from BASF Corporation) were used in Working Examples 1-2 and Comparative Examples 1-4. No retention aid was used in Working Example 3 and Comparative Example 5. The tensile strength of the papers made in these examples was measured according to TAPPI test method T404 and results of these measurements are shown in FIG. 1.

As shown in FIG. 1, the papers prepared using 3 parts of Acronal® NX 8777, which was prepared using maltodextrin, possessed greater tensile strength than the papers using 3 parts of Acronal® S728 NA or Acronal® 5504 NA, which were not prepared using maltodextrin. FIG. 1 also demonstrates that the use of a cationic retention aid and an elevated temperature (50° C.) increased the tensile strength of the resulting papers.

Working Examples 4-9

An aqueous suspension having 50 parts of Kraft pulp and 50 parts of groundwood pulp was prepared. 16 parts of hydrous kaolin or ground calcium carbonate (GCC) were used for paper glossiness: 16 parts of kaolin were added in Working Examples 5 and 7-8, and 16 parts of GCC were added in Working Examples 4, 6 and 9. 3 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 were used in all the examples as a polymer latex binder. For Working Examples 6-9, the Acronal® NX 8777 was added at 50° C., and for Examples 4-5, the Acronal® NX 8777 was added at room temperature. 0.3 parts based on the amount of copolymer dispersion added of Polymin® SNA were added in Working Examples 4-7 as a retention aid. No retention aid was used in Working Examples 8-9. The tensile strength of the papers made in these examples was measured and shown in FIG. 2.

In FIG. 2, the particular selection of the filler (whether hydrous kaolin or GCC) did not appear to affect tensile strength. The use of elevated temperature for the polymer latex binder addition also seems to have an effect in only one of the comparisons (Working Example 4 versus Working Example 6). The presence of the cationic retention aid, however, consistently resulted in increased tensile strength.

Working Example 10 & Comparative Examples 6-8

An aqueous suspension having 30 parts of Kraft pulp and 70 parts of groundwood pulp was prepared. 16 parts of GCC were added for paper glossiness. 5 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 were used in Working Example 10 as a polymer latex binder. 5 parts dry polymer based on the amount of dry cellulosic material of Acronal® 5728 NA were used in Comparative Example 6 as a polymer latex binder. 5 parts dry polymer based on the amount of dry cellulosic material of Acronal® 5504 NA were used in Comparative Example 7 as a polymer latex binder. No polymer latex binder was used in Comparative Example 8. The polymer latex binders were added at room temperature in all of the examples. 0.5 parts based on the amount of copolymer dispersion added of Polymin® SNA were used as a retention aid in Working Example 10 and Comparative Examples 6-7. No retention aid was used in Comparative Example 8. The tensile strength of the papers made in these examples was measured and shown in FIG. 3.

As shown in FIG. 3, the papers prepared using 5 parts of Acronal® NX 8777, which was prepared using maltodextrin, possessed greater tensile strength than the papers using 5 parts of Acronal® 5728 NA or Acronal® 5504 NA, and was not dependent on the presence of the cationic retention aid or the temperature at which the polymer latex binder was added.

Working Examples 11-27 & Comparative Examples 9-10

Aqueous suspensions having 50, 60, 70 or 80 parts of groundwood pulp and 50, 40, 30 or 20 parts of Kraft pulp were prepared. Working Examples 11-15 and Comparative Example 9 used the aqueous suspension having 50 parts of groundwood pulp and 50 parts of Kraft pulp; Working Examples 16-19 used the aqueous suspension having 60 parts of groundwood pulp and 40 parts of Kraft pulp; Working Examples 20-22 and Comparative Example 10 used the aqueous suspension having 70 parts of groundwood pulp and 30 parts of Kraft pulp; and Working Examples 23-27 used the aqueous suspension having 80 parts of groundwood pulp and 20 parts of Kraft pulp. 16 parts of GCC were added for paper glossiness. 0.5 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 were used in Working Example 27 as a polymer latex binder; 1 part dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 was used in Working Examples 11, 16, 20 and 23; 3 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 were used in Working Examples 12, 14-15, 17, 19, 21, 24 and 26; and 5 parts dry polymer based on the amount of dry cellulosic material of Acronal® NX 8777 were used in Working Examples 13, 18, 22 and 25. No polymer latex binder was used in Comparative Examples 9-10. For Working Examples 14-15, 19 and 26-27, the Acronal® NX 8777 was added at 50° C., and for the other examples, the Acronal® NX 8777 was added at room temperature. 0.1 parts based on the amount of copolymer dispersion added of Polymin® SNA were used as a retention aid in Working Examples 11, 16, 20 and 23; 0.3 parts based on the amount of copolymer dispersion added of Polymin® SNA were used in Working Examples 12, 14, 17, 19, 21, 24, and 26-27; and 0.5 parts based on the amount of copolymer dispersion added of Polymin® SNA were used in Working Examples 13, 18, 22 and 25. No retention aid was used in Working Example 15 and Comparative Examples 9-10. The tensile strength of the papers made in these examples was measured and shown in FIG. 4 and FIG. 5 (adjusted for basis weight).

As shown in FIGS. 4 and 5, increases in Acronal® NX 8777 and Polymin® SNA amounts resulted in increased in tensile strength of the resultant papers. In addition, as shown in these figures, the addition of the copolymer dispersion at an increased temperature (50 degrees C. versus room temperature) resulted in increased tensile strength.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Further, while only certain representative combinations of the formulations, methods, or products are disclosed herein are specifically described, other combinations of the method steps or combinations of elements of a composition or product are intended to fall within the scope of the appended claims. Thus a combination of steps, elements, or components may be explicitly mentioned herein; however, all other combinations of steps, elements, and components are included, even though not explicitly stated. 

1. A method of making paper, comprising: adding to an aqueous suspension containing pulp fibers a polymer latex binder comprising a copolymer obtained by polymerization of one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to 35 to form a mixture of the aqueous suspension and the polymer latex binder; and removing water from the mixture to form the paper.
 2. The method of claim 1, further comprising preparing the polymer latex binder by polymerizing in an aqueous medium a mixture of the one or more unsaturated monomers and the carbohydrate derived compound to produce the copolymer.
 3. The method of claim 1, wherein the carbohydrate derived compound is present in an amount of less than 50 wt % based on total monomer weight.
 4. The method of claim 1, wherein the carbohydrate derived compound is present in an amount of 5 to 45 wt % based on total monomer weight.
 5. The method of claim 1, wherein the copolymer is present in an amount of 2 to 12 wt % of the solids content of the mixture of the aqueous suspension and the polymer latex binder.
 6. The method of claim 1, wherein the copolymer comprises a pure acrylic copolymer, a styrene acrylic copolymer, a styrene butadiene copolymer, or a vinyl acrylic copolymer.
 7. The method of claim 1, wherein the one or more unsaturated monomers comprise an ethylenically unsaturated monomer.
 8. The method of any of claim 1, wherein the carbohydrate derived compound is selected from the group consisting of dextrins, maltodextrins, and mixtures thereof.
 9. The method of claim 1, wherein the carbohydrate derived compound has a weight average molecular weight of 3000 to 20,000.
 10. The method of claim 1, wherein the carbohydrate derived compound is soluble in water at room temperature in an amount of greater than 40% by weight.
 11. The method of claim 1, wherein a solution of the carbohydrate derived compound in an amount of 50% by weight in water at room temperature has a viscosity of 100 to 1000 cps.
 12. The method of claim 1, wherein the carbohydrate derived compound has a nonuniformity of 6 to
 12. 13. The method of claim 1, wherein the carbohydrate derived compound is chemically modified by etherification or esterification.
 14. The method of claim 1, further comprising adding one or more additional binders to the mixture.
 15. The method of claim 1, further comprising adding one or more cationic retention aids.
 16. The method of claim 15, wherein the one or more cationic aids comprise a polyethyleneimine containing polymer.
 17. The method of claim 1, wherein the aqueous suspension has less than 2 wt % solids when the polymer latex binder is added.
 18. The method of claim 1, wherein the polymer latex binder is added at a temperature of 40° C. to 80° C.
 19. The method of claim 1, wherein the polymer latex binder is added at a temperature of 45° C. to 70° C.
 20. A paper sheet, comprising: a matrix of pulp fibers having a copolymer uniformly dispersed throughout, said copolymer derived from one or more unsaturated monomers and a carbohydrate derived compound having a dextrose equivalent (DE) of 10 to
 35. 